System and method for forming porous bone filling material

ABSTRACT

A method for treating a vertebral bone comprises providing a gaseous substance and providing a flowable and settable bone filling material. The method further comprises introducing the gaseous substance into the bone filling material to form a porous bone augmentation material and inserting a material delivery device into the vertebral bone. The method further comprises injecting the porous bone augmentation material from the material delivery device and into the vertebral bone.

CROSS REFERENCE

The related applications, incorporated by reference herein are: U.S.Utility Patent Application Serial No. (Attorney Docket No.P0026126.00/31132.591), filed on Jan. 12, 2007 and entitled “System andMethod For Pressure Mixing Bone Filling Material” and U.S. UtilityPatent Application Serial No. (Attorney Docket No.P0026125.00/31132.590), filed on Jan. 12, 2007 and entitled “System andMethod For Forming Bone Filling Materials With Microparticles”.

BACKGROUND

Bone cements and other bone filling materials are currently usedthroughout the skeletal system to augment or replace bone weakened orlost to disease or injury. One example of a treatment that includes theadministration of bone filling material is vertebroplasty. Duringvertebroplasty, the cancellous bone of a vertebral body is supplementedwith bone filling material. Frequently, the available bone fillingmaterials do not possess material properties similar to the native bone.Materials, systems, and methods are needed to form and deliver bonefilling materials that may be selectively matched to the natural boneundergoing treatment.

SUMMARY

In one embodiment, a method for treating a vertebral bone comprisesproviding a gaseous substance and providing a flowable and settable bonefilling material. The method further comprises introducing the gaseoussubstance into the bone filling material to form a porous boneaugmentation material and inserting a material delivery device into thevertebral bone. The method further comprises injecting the porous boneaugmentation material from the material delivery device and into thevertebral bone.

In another embodiment a bone augmentation system comprises a firstvessel at least partially filled with a gaseous substance and a secondvessel at least partially filled with a flowable and settable bonefilling material. The system further comprises a mixing vessel in fluidcommunication with both the first and second vessels to receive thegaseous substance and the flowable and settable bone filling material.The mixing vessel includes a mixing mechanism for mixing the gaseoussubstance and the bone filling material to form a bone augmentationmaterial. The system also includes a dispensing instrument comprising adispensing reservoir for receiving the bone augmentation material andcomprising a cannulated member adapted to deliver the bone augmentationmaterial into a body region adjacent cancellous bone.

A method of augmenting a bone comprises pressurizing a gaseoussubstance, mixing the gaseous substance and a flowable bone fillingmaterial to form a bone augmentation material, injecting the boneaugmentation material into the bone, and allowing the bone augmentationmaterial to set to a hardened and porous condition within the bone.

Additional embodiments are included in the attached drawings and thedescription provided below.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a flowchart for a process of forming a modulated boneaugmentation material according to one embodiment of the disclosure.

FIG. 2 is a cross-sectional view of a material preparation systemaccording to one embodiment of the present disclosure.

FIG. 3 is a cross-sectional view of a material preparation systemaccording to another embodiment of the present disclosure.

FIG. 4 is a sagittal view of a section of a vertebral column.

FIG. 5 is a sagittal view of a section of a vertebral column undergoinga vertebroplasty procedure using a porous bone augmentation material.

FIGS. 6-7 are detailed views of the procedure of FIG. 5.

FIG. 8 is a sagittal view of a section of a vertebral column with anintervertebral disc treated with porous bone filling material.

DETAILED DESCRIPTION

The present disclosure relates generally to devices, methods andapparatus for augmenting bone, and more particularly, to methods andinstruments for augmenting bone with a porous material. For the purposesof promoting an understanding of the principles of the invention,reference will now be made to the embodiments, or examples, illustratedin the drawings and specific language will be used to describe the same.It will nevertheless be understood that no limitation of the scope ofthe invention is thereby intended. Any alterations and furthermodifications in the described embodiments, and any further applicationsof the principles of the invention as described herein are contemplatedas would normally occur to one skilled in the art to which the inventionrelates.

Referring first to FIG. 1, the reference numeral 10 refers to a methodfor forming a modified or modulated bone augmentation material that maybetter correspond to the material properties, including the modulus ofelasticity, of a target bone region as compared to unmodulated bonefilling material such as bone cement. At step 12, a gaseous substancemay be provided to a material preparation system 20 as shown in FIG. 2.Specifically, a vessel 22 may be filled with a gaseous substance 24 suchas air. The vessel 22 may be connected, either releasably or fixedly, toconnective tubing 26. In this embodiment, the vessel 22 has asyringe-like configuration, comprising a reservoir 28 which contains thegaseous substance 24 and a plunger 30 which may be moved through thereservoir 28 to pressurize the gaseous substance and to dispense thegaseous substance through the connective tubing 26. It is understoodthat in alternative embodiments, the contents of the vessel may bepressurized by any known means or alternatively, the gaseous substancemay be provided in prepackaged, pressurized form such as a compressedgas, such as carbon dioxide, nitrogen, or oxygen (as will be describedbelow).

Referring again to the method 10 of FIG. 1, at step 14, an appropriatebone filling material may be selected. Suitable bone filling materialsmay include polymethylmethacrylate (PMMA) bone cement, calcium phosphatebone cement, calcium sulfate compounds, calcium aluminate compounds,aluminum silicate compounds, hydroxyapatite compounds, in situ curableceramics or polymers, or other flowable materials that become more rigidafter delivery. Generally, before it is modified, the bone fillingmaterial may have a higher modulus of elasticity than the target boneregion. The bone filling material may be provided as multiple componentssuch as, a PMMA powder and a PMMA monomer. In FIG. 1, the order in whichthe gaseous substance and the bone filling material are introduced ismerely exemplary, and it is understood that the bone filling materialmay be introduced first or contemporaneously with the introduction ofthe gaseous material.

Referring again to FIG. 2, a bone filling material 32, which in thisembodiment is a bone cement, may be provided to the material preparationsystem 20. Specifically, a vessel 34 may be filled with the bone fillingmaterial 32. The vessel 34 may be connected, either releasably orfixedly, to the connective tubing 26. In this embodiment, the vessel 34has a syringe-like configuration, comprising a reservoir 36 whichcontains the bone filling material 32 and a plunger 38 which may bemoved through the reservoir 36 to dispense the bone filling material 32through the connective tubing 26. It is understood that in alternativeembodiments, the contents of the vessel may be pressurized by any knownmeans or alternatively, the gaseous substance may be provided inprepackaged, pressurized form.

Referring again to FIGS. 1 and 2, at step 16 the gaseous substance 24may flow through the connective tubing 26 and into a mixing vessel 40where it becomes introduced into the liquid bone filling material 32which has traveled through the tubing 26 from the vessel 34. In thisembodiment, the mixing vessel 40 may be a static mixer comprising fixedmixing elements 42. As the two flow streams of gas 24 and bone fillingmaterial 32 move through the static mixer 40, buffeted by the mixingelements 42, bubbles of the gaseous substance 24 may form within andbecome dispersed throughout the bone filling material 32 to form aporous modulated bone augmentation material 43. The gaseous substance 24may be added until the concentration of bubbles in the liquid boneaugmentation material 43 is sufficient to lower the overall modulus ofelasticity of the final cured or hardened modulated bone augmentationmaterial to a level that more closely matches the modulus of the targetbone region or that at least reduces the risk of damage to the adjacentbone that could otherwise be caused by the unmodulated bone cement. Incertain patients, it may be desirable to reduce the modulus ofelasticity to a level lower than natural cancellous bone. For example, amodulus of elasticity for hardened bone augmentation material that isless than five times that of cancellous bone may be suitable for somepatients.

In alternative embodiments, a more active form of mixing may be used.For example, the mixing vessel may comprise an agitator for mixing thegaseous substance and the bone filling material. Alternatively, a gasdiffuser or aerator may be used to disperse the gaseous substancethroughout the bone filling material.

In the embodiment of FIG. 2, the material preparation system 20 mayfurther include a control mechanism 44, such as a valve, to control theflow of the gaseous substance 24 into the mixing vessel 40. With thevalve 44 in an open position, a continuous flow of gaseous substance 24may be dispensed from the vessel 22 into the mixing vessel 40. The valve44 may also be toggled between open and closed positions to provideintermittent bursts of gas flow. Further, the valve 44 may be used tocontrol the velocity of the flowing gaseous substance 24 and thepressure within the vessel 22.

Thus, by controlling the continuity, rate, and pressure of the gaseousphase substance 24, the control valve 44 may be used to control the sizeand density of the bubbles that form in the fluid modulated boneaugmentation material, and ultimately the size and density of the poresthat are formed in the hardened modulated bone augmentation material.For example, larger pores may impart a lower modulus than the samequantity of smaller pores. A higher density of pores may impart a lowermodulus to the bone filling material than would a less dense array ofpores of the same size and material properties.

The desired size and density of the pores may be dependent upon the sizeof the target bone region and characteristics of the patient includingthe age, bone density, body mass index, or health of the patient. Forexample, an elderly osteoporotic vertebroplasty patient may require amore reduced modulus bone augmentation material than would a younghealthy trauma victim undergoing a similar procedure. The size of thepores may be selected based upon the patient and controlled bypressurization, flow rate, a pattern of intermittent introduction of thegaseous substance, or other means. For example, 90% of the pores may bein the range of 1 to 2000 microns in diameter. Other suitable pore sizesmay range from 10 to 1000 microns.

Other additives may be added to the bone filling material during thepreparation of the bone filling material or during the mixing of thegaseous substance. Additives that include radiocontrast media may beadded to the bone filling material to aid in visualizing the boneaugmentation material with imaging equipment. Suitable radiocontrastmaterials may include barium sulfate, tungsten, tantalum, or titanium.Osteoconductive or osteoinductive materials may be added to promote bonegrowth into the hardened bone augmentation material. Suitableosteoconductive materials may include hydroxyapatite (HA), tricalciumphosphate (TCP), HA-TCP, calcium phosphate, calcium sulfate, calciumcarbonate, and/or bioactive glasses. Suitable osteoinductive materialsmay include proteins from transforming growth factor (TGF) betasuperfamily, or bone-morphogenic proteins, such as BMP2 or BMP7.Pharmacological agents may be added to promote healing and prevent orfight infection. Suitable pharmacological additives may includeantibiotics, anti-inflammatory drugs, or analgesics.

Referring again to FIG. 1, at step 18, the modulated bone augmentationmaterial may be delivered into a target bone region in a patient'sanatomy. The modulated bone augmentation material may be transferred toa delivery system, such as a syringe or a threaded material dispensingsystem prior to delivery into the target bone region. In alternativeembodiments, the bone filling material and the gaseous substance may bemixed in the same container that will be used to dispense the mixturesuch that a material transfer becomes unnecessary. In still anotheralternative embodiment, a gas cartridge can be directly attached to thedelivery nozzle of a known bone cement delivery instrument.

Although the target bone region will often be in a bone, other boneregions, such as joints, may receive the modulated bone augmentationmaterial to, for example, promote fusion. Examples of target boneregions may be fractured cortical or cancellous bone, osteoporoticcancellous bone, or degenerated intervertebral discs. By matching themodulated bone augmentation material to the material properties of theadjacent bone, complications associated with unaltered, high modulusbone cements may be minimized. In particular, matching the materialproperties may provide a uniform stress distribution, minimizingsignificant stress concentrations that may pose a fracture risk toadjacent bone.

Referring now to FIG. 3, in an alternative embodiment, a materialpreparation system 50 may be substantially similar to the system 20 withthe differences to be described. In this embodiment, a vessel 52 may befilled with a compressed gaseous substance 53 such as carbon dioxide. Asdescribed above in method 10, the gaseous substance 53 may flow into amixing vessel 56 where it may be dispersed throughout a bone fillingmaterial 54 from a vessel 55. The vessel 52 may be removable fromconnective tubing 58 through the use of quick-connect fasteners,threaded fasteners, clamp fasteners, or other suitable fasteners. Thus,the gaseous substance 53 may be provided in a pre-measured, pre-filled,pre-pressurized interchangeable cartridge format that may simplify thebone augmentation material preparation process.

Referring now to FIG. 4, in one embodiment, a modulated boneaugmentation material formed by method 10 may be used to augment orreplace portions of a vertebral column. The reference numeral 60 refersto a healthy vertebral joint section of a vertebral column. The jointsection 60 includes adjacent vertebrae 62, 64 having vertebral bodies66, 68, respectively. An intervertebral disc 70 extends between thevertebral bodies 66, 68. Although FIG. 4 generally depicts a lumbarregion of the spine, it is understood that the systems, materials, andmethods of this disclosure may be used in other regions of the vertebralcolumn including the thoracic or cervical regions.

Referring now to FIGS. 5-7, due to traumatic injury, cancer,osteoporosis or other afflictions, the vertebral body portion 68 of thevertebra 64 may begin to collapse, causing pain and loss of bone height.One procedure for restoring the vertebral height, reducing pain, and/orbuilding mass is known as vertebroplasty. In a vertebroplasty procedureaccording to one embodiment of this disclosure, a stylet or othersharpened instrument (not shown) may be inserted into an injectioninstrument such as a cannula 72 and arranged so that a sharpened tipprotrudes through the end of the cannula. The assembled stylet andcannula 72 may then be inserted through a pedicle of the vertebra 64 andinto the cancellous bone of the vertebral body 68. This insertion may beguided through the use of fluoroscopy or other imaging modalities. Withthe cannula 72 in place in the vertebral body 68, the stylet may bewithdrawn leaving the cannula in place to serve as a pathway fordelivering instruments or materials into the bone. In alternativeembodiments, a surgical needle having a cannulated body and a pointedtip may be used to access the vertebral body.

Following the method 10, described above, a modulated bone augmentationmaterial 74 comprised of bone cement 76 and bubbles of gaseous substance78 may be formed and transferred to a delivery system 80. The deliverysystem 80 may be a conventional syringe, having a material reservoir anda plunger mechanism movable therethrough, or a more sophisticatedthreaded injection system such as the type covered by, for example, U.S.Pat. No. 6,348,055 which is incorporated by reference herein. Othertypes of material delivery systems may also be suitable. The deliverysystem 80 may be actuated, such as by moving the plunger mechanism intothe material reservoir, to move the bone augmentation material 74through the cannula 72 and into the vertebra 64 where the mixture mayflow into the interstices of the cancellous bone of the vertebral body68 as shown in FIG. 7. It is understood that the bubbles of gaseoussubstance 78 shown in FIG. 7 are not necessarily to scale but rather aremerely exemplary of the random disbursement of the bubbles of gaseoussubstance which will later form pores within the hardened boneaugmentation material. As described above, within any given mixture ofmodulated bone augmentation material, the pores may have different sizesand/or properties. Further, the density of pores may be determined basedupon the amount the original bone filling material must be modified toachieve an acceptable modulated bone augmentation material.

With the bubbles of gaseous substance 78 distributed throughout the bonecement 76, the modulated bone augmentation material 74 may be cured orotherwise allowed to harden within the vertebral body 68. The bubbles ofgaseous substance 78 may remain suspended in the hardened bone cement76, forming pores which reduce the overall stiffness of the modulatedbone augmentation material 74. The modulus of elasticity of the hardenedmodulated bone augmentation material 74 may be lower than that of theunmodulated hardened bone filling material 76, alone, and closer to themodulus of elasticity of the cancellous bone of the vertebral body 68than that of the hardened bone filling material alone. Thus, thematerial 74 creates a more uniform stiffness in the vertebral body 68,avoiding the significant alterations in stress distribution that wouldbe associated with the use of bone cement alone. The more uniformstiffness in the vertebral body 68 may lower the risk for fracture inthe adjacent vertebrae.

Although the use of the modulated bone augmentation material 74 has beendescribed for use in a vertebroplasty procedure, it is understood thatin alternative treatments, channels or voids may be formed in thevertebral body using probes, balloons, drills, cutting blades or otherdevices. In these embodiments, the mixture of gaseous bubbles and bonefilling material may be used to fill the preformed voids or channels.The resulting reduced modulus material may be particularly effective inthese embodiments as the otherwise unmodulated, large concentrations ofbone cement accumulating in the preformed voids may give rise tosignificant alteration is the stress distribution.

Although the use of modulated bone augmentation material has beendescribed primarily for vertebral body applications, it is understoodthat the same modulated material may be used for other procedures wherereduced modulus bone cement may be desirable. For example, the modulatedmaterial may be useful for fracture repair.

In one alternative embodiment, a modulated bone augmentation material81, including gaseous bubbles 82, may be created using the method 10 andmay be used to fuse the joint section 60. The fusion of the joint 60 maybe accomplished using conventional fusion techniques includingtransforaminal lumbar interbody fusion (TLIF), posterior lumbarinterbody fusion (PLIF), or anterior lumbar interbody fusion (ALIF)procedures. Such techniques may involve the use of cages or otherintervertebral spacers to maintain the height of the disc space. As asupplement or replacement for the bone graft or bone cement that wouldotherwise be used in a spinal fusion procedure, the modulated material81 may be injected into the disc 70 or the disc space remaining afterthe removal of disc 70. The modulated material 81 may flow intocrevices, voids, or prepared areas of the adjacent vertebral endplates.After hardening, the material 81 may have a modulus of elasticitysimilar to that of the adjacent endplates of the vertebrae 62, 64, or atleast lower than unmodulated bone cement. Use of the modulated material81 may reduce the risk of the hardened material subsiding into theendplates of the adjacent vertebrae 62, 64.

Although only a few exemplary embodiments have been described in detailabove, those skilled in the art will readily appreciate that manymodifications are possible in the exemplary embodiments withoutmaterially departing from the novel teachings and advantages of thisdisclosure. Accordingly, all such modifications and alternative areintended to be included within the scope of the invention as defined inthe following claims. Those skilled in the art should also realize thatsuch modifications and equivalent constructions or methods do not departfrom the spirit and scope of the present disclosure, and that they maymake various changes, substitutions, and alterations herein withoutdeparting from the spirit and scope of the present disclosure. It isunderstood that all spatial references, such as “horizontal,”“vertical,” “top,” “upper,” “lower,” “bottom,” “left,” “right,”“anterior,” “posterior,” “superior,” “inferior,” “upper,” and “lower”are for illustrative purposes only and can be varied within the scope ofthe disclosure. In the claims, means-plus-function clauses are intendedto cover the elements described herein as performing the recitedfunction and not only structural equivalents, but also equivalentelements.

1.-24. (canceled)
 25. A bone augmentation system comprising: a firstvessel at least partially filled with a gaseous substance; a secondvessel at least partially filled with a flowable and settable bonefilling material; a mixing vessel in fluid communication with both thefirst and second vessels to receive the gaseous substance and theflowable and settable bone filling material, the mixing vessel includinga mixing mechanism for mixing the gaseous substance and the bone fillingmaterial to form a bone augmentation material; and a dispensinginstrument comprising a dispensing reservoir for receiving the boneaugmentation material and comprising a cannulated member adapted todeliver the bone augmentation material into a body region adjacentcancellous bone.
 26. The bone augmentation system of claim 25 furthercomprising: a control mechanism disposed between the first vessel andthe mixing vessel.
 27. The bone augmentation system of claim 26 whereinthe control mechanism comprises a valve adapted to regulate the flow ofthe gaseous substance.
 28. The bone augmentation system of claim 25wherein the mixing mechanism comprises a plurality of static mixingelements.
 29. The bone augmentation system of claim 25 wherein themixing mechanism comprises a gas diffuser.
 30. The bone augmentationsystem of claim 25 wherein the mixing mechanism comprises an agitator.31. The bone augmentation system of claim 25 wherein the second vesselcomprises a material reservoir and a plunger member movable through thematerial reservoir to push at least a portion of the flowable andsettable bone filling material from the material reservoir.
 32. The boneaugmentation system of claim 25 wherein the first vessel is apressurized cartridge of carbon dioxide.
 33. The bone augmentationsystem of claim 25 wherein the first vessel comprises a materialreservoir and a plunger member movable through the material reservoir topush at least a portion of the gaseous substance from the materialreservoir. 34.-36. (canceled)